This invention pertains to hermetic rotary compressors for compressing refrigerant in refrigeration systems such as refrigerators, freezers, air conditioners and the like. In particular, this invention relates to reducing frictional loading of the sliding vanes on the piston.
In general, prior art rotary hermetic compressors comprise a housing in which are positioned a motor and compressor cylinder. The motor drives a crankshaft for revolving a rotor or roller (piston) inside the cylinder. One or more sliding vanes are slidably received in slots located through the cylinder walls. The vanes, cooperating with the rotor and cylinder walls, provide the structure for compressing refrigerant within the cylinder bore.
The operating parts of rotary hermetic compressors are machined to extremely close tolerances and the surfaces of the parts are finished to a high degree in order to prevent leakage and provide a very efficient compressor. Preventing leakage of refrigerant from high pressure areas to low pressure areas is of main concern to increase compressor efficiency.
One of the problems encountered in prior art hermetic compressor arrangements has been high frictional loading between the vane tips and the rolling piston, and between the piston and the cylinder walls. The vane necessarily has to be highly loaded against the piston to prevent leaks. At times, insufficient oil reaches the critical wear areas of the vane tips and piston, thereby increasing the wear rate of both. A reduction in the frictional loading on the vane tips would reduce wear and increase compressor efficiency.
Further, the rolling of the piston beneath the vane tip causes worn areas on the piston circumference. These worn areas lead to the creation of leak paths between the piston and cylinder wall during compressor operation. There is a need for a compressor that exhibits a high resistance to piston wear caused by the engaging vanes sealing.
Normally, the refrigerant within the compressor system is in the gaseous state. At times, the system pressure creates an overpressure condition which changes the refrigerant from gas to liquid. When the compressor encounters refrigerant, this is called slugging. Slugging of liquid refrigerant within a compressor can damage the relatively fragile discharge and suction valves along with other compressor components.
Some prior art hermetic compressors have not included mechanisms for protection from slugging conditions. One such compressor is that shown in U.S. Pat. No. 2,800,274. It shows a piston that operates within a cylinder bore having a vane pivotable attached to the piston. The vane prevents piston rotation. Because of this construction, during a slugging condition the vane does not have the ability to separate from the piston and connect together suction and discharge pressure areas. This may cause liquid to forcibly pass by the discharge valve to an extent that it may damage the valve and other compressor parts. An important design consideration for a compressor is to operate without failure, during a momentary slugging condition.
The present invention is directed to overcoming the aforementioned problems associated with rotary compressors, wherein it is desired to provide a pin inserted into the piston to prevent piston rotation and cause the vane to engage the piston at substantially one point, thereby reducing frictional loading and wear about the circumference of the piston.